Allow setting of api_workers parameter for neutron config file

[Shiv Haris]

Parameter api_workers in the default section is not being set by neutron.

Allow this to be set if API_WORKERS variable is set, usually in local.conf

If this variable is not set, let neutron initialization use whatever it deems necessary, depending on cpu cores etc. Leave it to that code to decide the appropriate value. However user's explicit specification in local.conf should take precedence.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/164438

[OpenStack Infra (hudson-openstack)]

Change abandoned by Ian Wienand (<email address hidden>) on branch: master
Review: https://review.openstack.org/164438
Reason: We have the same thing in I7ede29430923b0983b20ab27d9f3b7244deaa477

Please update that; it seems the dependent change is merged but neutron people should definitely weigh in before it is merged

[OpenStack Infra (hudson-openstack)]

Change abandoned by Russell Bryant (<email address hidden>) on branch: master
Review: https://review.openstack.org/140482

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/191126

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/191126
Committed: https://git.openstack.org/cgit/openstack-dev/devstack/commit/?id=e155b894c8975f649cbbbc08675095fe728d0b69
Submitter: Jenkins
Branch: master

commit e155b894c8975f649cbbbc08675095fe728d0b69
Author: armando-migliaccio <email address hidden>
Date: Fri Jun 12 08:55:02 2015 -0700

    Set Neutron api_workers to $API_WORKERS

    Change [1] brings back this feature in Neutron, so we want to have
    the ability to set the number of API workers the same way other
    projects do.

    However, this cause some instability, so we need to be careful on
    how we bring it back.

    [1] https://review.openstack.org/#/c/191127/

    Closes-Bug: #1432189
    Related-bug: #1432065

    Change-Id: Id4986a49d33fa4b8a7291150488665e200525dac
    Co-authored-by: Russell Bryant <email address hidden>